DETERMINATION OF THE MAGNETIC-SUSCEPTIBILITY OF LABELED PARTICLES BY VIDEO IMAGING

Magnetic cell sorting is gaining in popularity as a method to separate and recover viable cells which differ in functionality, but not in ph ysical characteristics. We are developing a continuous cell sorter to overcome the restrictions of current batch methods, which are limited in their throughput and separation efficiency and which can also subje ct cells to potentially detrimental physical stresses. Of primary impo rtance in the design and operation of a continuous magnetic cell sorte r is the degree of cell magnetization, which is characterized by a pro perty called the magnetic susceptibility. Current techniques for measu ring susceptibility give only population average values. We describe h ere a video-based technique for quickly measuring the susceptibility o f large numbers of individual particles. Paramagnetic particles are pu mped across the interpolar gap of a permanent magnet and the magnetic held-induced deflections are recorded by video microscopy. Susceptibil ity is computed from force balances and the measured velocities for in dividual particles. Our results show that this method can provide susc eptibility values which agree well with values obtained from other est ablished methods, while additionally providing population statistics n ot available by the other methods. The versatility of this method is a lso demonstrated.